The present invention pertains to a system for sychronizing the location of splices in the component webs of a composite web and, more particularly, to a method and apparatus for synchronizing the splices in the component webs used to make a composite corrugated paperboard web so that the splices defining an order change are substantially coincident in the paperboard web and may be simultaneously cut out and diverted as scrap.
In a system for making corrugated paperboard in which multiple paper webs are sequentially glued together, unusable scrap may occur for a number of reasons. Defects in the form of tears or other discontinuities in the component paper webs is one source. A lack of adhesive or inadequate adhesive between joining component webs may also result in defects in the composite paperboard web. Scrap is also unavoidably generated where two webs are joined with a splice, either to renew the supply of one of the component webs or to change a characteristic of one of the component webs as at order change.
Because a typical composite paperboard web includes at least two component webs, in the case of "single face" material, and because more typically a composite paperboard web includes at least three component webs, as in so-called "double face" paperboard, web splices are required quite often and each splice must be detected in the completed paperboard web, cut out in a short longitudinal section defined by a pair of spaced transverse cuts, and diverted as scrap. Attempts have long been made in the prior art to accomplish the ideal goal of synchronizing all of the splices in the component webs so that the splices coincide at the same point in the finished composite paperboard web so they may be simultaneously cut out in a single piece of scrap. However, the variable processing ,conditions to which each component web is typically subject in a corrugator wet end where the composite web is formed make web measurement and, therefore splice synchronization, very difficult. For example, in the manufacture of a typical double face paperboard web, a liner web and a corrugated medium web are supplied from separate sources, each of which includes a splicer and a variable length storage or takeup section. The liner and medium webs are brought together in a single facer apparatus and secured by adhesive applied to the corrugated medium upstream of the single facer. The single face web is initially directed to another variable length storage section commonly referred to as a "bridge" from which it is fed at varying rates to be joined with a second liner web in a double facer apparatus to complete the double face corrugated web. Adhesive is applied to the exposed corrugated medium of the single face material after it is drawn out of the bridge before entry into the double facer. The second liner web also travels through a variable length storage section prior to being brought into contact with the adhesive-coated flutes of the single face material in the double facer.
An expanded system used for the production of so-called "double wall" paperboard utilizes an additional single facer and the associated sources of liner and medium webs, each also having its own splicer and variable storage sections, as well as a separate bridge for the second single face web. The single facer and double facer are independently driven and controlled, with the double facer operation dictated by downstream processing requirements such as slitting, cutting, and stacking which comprise certain of the operations in the dry end of the corrugator; whereas, control of operation of the single facer is dictated by maintenance of an adequate bridge storage to accommodate increases in speed of the double facer and to allow the speed of delivery of the liner and medium webs to be decreased to accommodate the requirements of splicer operation. It will be appreciated, therefore, that all of the foregoing variables have made it extremely difficult to synchronize the splices in the component webs of a double face paperboard web. The problems are, of course, increased where an additional single facer is added to the system to manufacture double wall paperboard.
The prior art discloses a number of corrugator control systems which are intended to reduce scrap by synchronizing the splices in the component webs to be simultaneously cut out at order change. Although these systems address certain of the problems associated with accurate splice synchronization, none of them adequately addresses web length monitoring and control, as well as monitoring and control of related processing equipment, in a manner which assures accurate splice synchronization in the composite paperboard web as it moves from the corrugator wet end into the dry end.
U.S. Pat. No. 4,284,445 describes a method and apparatus for coordinating the splices in all web components of a corrugator system to synchronize the splices so that they may be cut out nearly simultaneously to minimize scrap at order change. This system utilizes pulse generators in contact with the component webs at points just upstream of the single facer and the double facer to continuously track component web lengths. The length of single face material deposited in the bridge is tracked by a photo detector system which senses the height and positioning of the loops or folds in the single face material as it accumulates on and moves along a belt conveyor in the bridge. The remaining order length is monitored at the downstream web cut off apparatus and is continuously compared with the component wet lengths being processed in the web end, so that at order change the upstream ends of each component web (presumably spliced to a new component web for the next order) all arrive at the cut off apparatus simultaneously. However, this system does not take into consideration or in any way accommodate the variable component web storage between each splicer and the respective single facer or double facer apparatus. In addition, the method used to detect and measure the length of single face material in the bridge, though possibly accurate enough to utilize as a control parameter for single facer speed, is not believed to be accurate enough a measurement technique for splice synchronization.
U.S. Pat. No. 4,576,663 also discloses a method and apparatus for corrugator wet end control which is intended to synchronize the splices in the component web materials so that the splices substantially coincide to minimize scrap and production down time. As in the above identified prior art patent, the system in this patent also utilizes pulse generators to continuously track the length of certain of the component webs brought together to form the composite paperboard web. Specifically, web lengths are monitored at the medium splicer (or medium splicers in a multi-wall paperboard system), at the double facer liner splicer and at the downstream cut off apparatus. Single face web accumulation in the bridge is monitored with a photoelectric device which senses an optimum storage value and the single facer speed is controlled to maintain that optimum value by adjusting the value in accordance with lengths measured by the pulse generators at the medium splicer and the double facer splicer. An initial web length determination is made for the upstream-most medium web component between its splicer and the downstream cut off apparatus. Once that length determination is made, the lengths of all other web components, including the liner web component to be joined with that medium web component, the liner web added in the double facer, and the component webs for any additional single face component of the composite web, are all based on the initial length determination for the upstream-most medium web component. The calculations utilize premeasured fixed distance components and running web lengths measured by the various pulse generators as modified by bridge storage adjustments mentioned above. The timing of operation of the various web splicers in the system are all based on the initial operation of the upstream-most medium web splicer. In addition, none of the dynamic web length measurements take into account the continuously varying storage length in the takeup or dancer roll associated with each component web splicer. In addition, compensation for variable wrap arm adjustments in the single facers are not accounted for. As a result, there are inherent significant errors in the initial and dependent web length measurements and, because the timed sequence of operation of the various splicers in a downstream direction is based on sequential use of the various measured lengths, there is an error accumulation in the sequential downstream operation of the remaining splicers.
In addition to the variations mentioned above which are not addressed in prior art systems, it is also known that the response time of each of the several splicers in a corrugator wet end system may vary from the response time of the others. Thus, the time between generation of a splice operation signal and the actual execution of the splice by the splicer will vary from one machine to another, even if the splicers are of identical types, depending on such things as relative wear and the like. In addition, the response time of a splicer will normally change over time. Failure to account for such variations also leads to inaccuracies in attempts to synchronize splice location in the completed paperboard web. Each of the splices may be about 5 inches (13 cm) in length and it is desirable to synchronize the splices so that they are all within about three feet (1 meter) of one another to minimize the length of the piece of scrap cut out and diverted from the system.
Therefore, there is a real need for an accurate splice synchronization system for a corrugator wet end operation which will provide accurate and repeatable synchronization of component web splices at order change. Any such system must, of necessity, include means for accurately determining the dynamic real time lengths of each of the multiple component webs, the lengths of each of which are subject to continuous length variation during corrugator operation. Ideally, a web synchronization system should also include means for initially and periodically calibrating the system to account for inevitable errors in measurement attributable to changes in typical web length measuring devices.